PPFD（光合光子通量密度）测量每秒到达植物表面的光合有效光（400–700 nm）的数量，以微摩尔/平方米/秒（µmol/m²/s）表示。 它是比较植物生长灯强度和效率的最准确指标。
关键事实
- Measures light in the photosynthetically active radiation (PAR) range: 400–700 nm
- Unit: µmol/m²/s — how many photons hit one square metre of canopy per second
- Leafy greens thrive at 150–250 µmol/m²/s; fruiting crops need 400–800+
- PPFD varies with distance from the light source — measure at canopy height
- More useful than wattage for comparing grow lights across brands and technologies
- Daily light integral (DLI) = PPFD × hours of light — the total daily photon dose